Method of making magnetic bodies



lee-84 Patented Feb. 20, 1934 UFOSS UNITED STATES Reference PATENT OFFICE METHOD OF MAKING MAGNETIC BODIES Charles (7. Neighbors, Chicago, Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application December 11, 1931 Serial No. 580,503

'11 Claims.

This invention relates to a method of makin magnetic bodies and more particularly magnetic bodies made of finely divided magnetic material.

-An object of the invention is to provide a method of producing magnetic bodies having improved magnetic properties and low energy losses.

Magnetic cores formed of finely divided and individually insulated particles of magnetic material are extensively used in loading coils for improving the transmission characteristics of telephone lines. In the construction of such cores the finely divided magnetic material is mixed with an insulating material which serves also as a binder and the mixture is subjected to a pressure of substantially 200,000 pounds per square inch to form the component material into a substantially homogeneous mass having a high degree of mechanical strength. In cores of this type, particularly those in which the magnetic material is a nickel-iron alloy, the insulating material must be of such a character as to be able to withstand the heat-treatment and mechanical operations to which the material is subjected in forming the cores and developing the magnetic properties of the material.

In accordance with one embodiment of the present invention,,magnetic material in finely divided form is mixe w1 spur-tron of insulat' ma 'l acid, such as tartaric acid anifa'dditioifal -ingfedients, such silicate, talc and kaolin. The insulating materialis'thbroughly mixed with the particles of magnetic material and the entire mass is evaporated to complete dryness. The coated particles artliii mi xed'withasecond portion of the insulating material and again the mass isglellt fated'fifiiompletefdryness. A third coating is then applied in the same manner and the material is then pressed into suitable cores which are annealed to relieve the mechanical strains in the material and improve the magnetic properties 'of the cores. I

In practicing the present invention, the magnetic material is preferably prepared from a brittle alloy containing nickel and irgn, with or with- 011 e addition of 0 er constituents, and commonly known as ggmalloyl. The alloy may be prepared in the manner described in Patent No. 1,669,649 issued May 15, 1928 to C. P. Beath and H. M. E. Heinicke. wherein approximately 81 parts of nickel and 19 parts of ironare melted together in an oxidizing atmosphere, the resulting alloy being poured into a mold. The alloy thus".

consisting of a water solube organic (Cl. 1'l521) I fine crystalline structure which is desirable since the disintegration of the. material takes place at the crystal boundaries and, consequently, the smaller the size of the crystals the finer the dust which can be produced therefrom. The slabs are then reduced to a finely divided form in any suitable manner and the finely divided alloy is subsequently reduced to a dust by pulverizing it in an attrition or ball mill.

The dust from the attrition or ball mill is then sifted and the portion passing through a 120- mesh screen is placed in a closed container and annealed at a temperature of approximately 885 C. The annealed dust is removed from the container in the form of a cake, which is again reduced to a. powder by crushing it in a rotary crusher and subsequently grinding it in an attrition mill, the ground dust is again sifted through a 120 mesh screen and the dust passing the screen is then mixed with the insulating composition as described hereinafter. It should be understood, however, that the present invention suitable for the purposes of the pres en't' invention, the following formula is given: I

Pounds Tartaric acid .30 Sodium silicate 1,05 Powdered talc .75 Kaolin .75 Water- 12.00

The ratio of acid to sodium silicate, as given in the above formula, is 1:3/2 but may range from 1:3 to 1:8 or upwards, the effectiveness of the insulation decreasing somewhat as the ratio of acid to sodium silicate decreases from that given in the above formula. The ratio of the solid materialsJtalc and kaolin) to the watersoluble r r iaterials (acid and sodium silicateT'fiYay variedwiiielg as may also the ratio of t'vatei" td the other ingredients, the water being used merely to dissolve the water-soluble materials and to give the desired consistency 'to the mixture of insulating composition and dust.

The 33,911 specified in the above formula is a binder n'd has the function of preventing cracks the finished core parts, in addition to a, an

Urinal being a rather eii'ective insulating material. In certain cases it may be omitted, depending upon the characteristics dsifed'iii'the finished core parts.

The permalloy dust thus obtained is thoroughly mixed with a portion oi insulating material. It has been found that best results are obtained by applying the insulating material in two to live successive steps. This makes it possible to use a smaller amount oi insulating material and still obtain a better insulation oi the particles. The smaller amount oi insulating material used also increases the permeability oi the magnetic body because permeability is proportional to the amount oi insulating material used. The total amount oi insulating material may be as low as oi the amount oi dust used according to the permeability desired.

For convenience the total amount oi insulating material used is usually divided into a number oi parts equal to the number oi coatings to be applied, although it has been iound by experiment that when the coatings are applied in successively increasing amounts better results are obtained than when the coatings are applied in equal amounts. As an example oi using successively increasing amounts of insulating material per coating when the amount oi insulating material is 3.2% oi-permalloy dust by weight, a quantity oi permalloy dust is first mixed with a quantity of insulating material comprising .50% oi the quantity oi dust by weight. The mixture is then evaporated to a condition oi complete dryness in order to obtain the maximum insulating resistance and isstirred constantly to prevent caking and to insure a thorough coating oi the individual dust particles. To obtain a complete drying of the magnetic material, its temperature may be raised to 120C" and even much higher temperatures may be used without injury to the material. The material aiter being thoroughly dried has a very low afllnity ior water, so that no special protection need be provided against the absorption oi water by the material.

Aiter the application oi the first coating, the coated particles are again mixed with about 1.0% oi the insulating material in the same manner and the material is then again evaporated to dryness. In applying the third coat, 1.7% oi insulating material is added to the double coated par! ticles and the mixture is again evaporated to complete dryness.

It is importantin this method that each coating be rendered insoluble by drying beiore the next coating is applied, otherwise the application oi a subsequent coating would tend to redissolve the previously applied coating and destroy the eii'ectiveness oi the multiple coating.

The insulated dust is siited through a 16-mesh screen, placed in a mold and compressed into core parts under a pressure oi approximately 200,000 pounds per square inch. The core parts are then transferred to an annealing furnace where they are annealed to relieve the internal stresses set up by the pressing operation and thereby to produce a core having low hysteresis loss and high permeability. The annealing temperature used is preierably about 500 0., but a temperature as high as 565 C. may beused without destroying the eiiectiveness oi the insulation. Where a temperature oi 500 is used, the core parts are preferably raised to that temperature in about twenty minutes and maintained at such temperatue ior about iive minutes. T e e annealing temperatures and periods may vary with cores oi different sizes. Ii higher annealing temperatures are used, the time should, oi course, be proportionately shortened and vice versa.

The drying and annealing temperatures apparently drive oii substantially all of the volatile constituents oi the material, including the organic acid, in the iorm oi gases, with the result that the annealed core parts contain only the end-products oi the heating process and contain no water-absorbent substances. This makes it unnecmsary to wash' and dry the core parts aiter annealing to remove such water-absorbent substances. The tartaric acid used is a very weak oxidizing agent and, since it volatilizes at a relatively low temperature, very little oxidation oi the metal takes place during the annealing operation. Such oxidation may be objectionable in some cases since it appears to aflect uniavorably the magnetic iualities oi the finished cores.

As an example oi the eflect oi the triple coating oi the dust particles, the iollowing results oi tests made on core rings commonly referred to as 75 permeability cores are given. Three batches oi core rings were made up and a single coating oi insulating material was applied to one set, a double coating was applied to the second set, and a triple coating was applied to the 118 It will be noted that the total amount oi insulating material used in the double coated batch oi rings was less than for the single coated batch, and the total amount oi insulating material used in the triple coated batch was less 120 than used in either the single or double coated batch. Due to the high resistance of the core material when the triple coating oi insulation is applied, it is evident that the energy losses due to eddy currents in the core will be extremely Another test oi multiple coatings was made on magnetic dust particles made in accordance with the disclosure oi the patent to White et al.,'No. 1,787,606, January 6, 1931, using 2% molybdenum and 4% copper in the magnetic alloy from which the dust was made with the iollowlng results:

Eddy Resist- Pcmeaanoe bility m, 188

'Numbu' oi The total amount oi insulation in each case was 1.2% oi the dust by weight. These cores were considerably smaller than those oi the previous example which accounts ior the lower resistance of these cores. However, it will be noted that the 166 resistance increased enormously and consistently with the increased number oi coatings.

The standard amount oi insulation used heretoiore has been about 3.2% oi the dust by weight. The use oi the multiple coating indicates that Cross Reference much smaller amounts of insulating materials may be used for a particular resistance of the cores and as pointed out above the less insulating material used the higher ill be the permeability of the cores. Y

One or more core parts thus formed are then used to constitute a core to which the usual toroidal winding is applied to form a loading coil, the number of core parts used depending upon the electrical characteristics of the circuit with which the loading coil is to be associated.

In place of the tartaric acid specified, in the above formula, any other suitable water-soluble organic acidy e use a oug s pre- 1cm 5 use a non-corrosive non-irritating nonoxidizing or anic acid and'one which leaves a non-Egroscopic residue, such as tartaric, lactic andcitric acids. Other suitable acids which may be used are succinic, oxalic, and malonic acids.

The invention is not limited to e-embc ments above described but may be varied widely within the scope of the following claims.

What is claimed is:

l. A method of producing a magnetic body which consists of mixing finely divided dust particles with an insulating material including an organic acid, drying the mixture, mixing a second quantity 01 said insulating material with the resulting product and again drying the mixure.

2. A method of producing a magnetic body from finely divided magnetic particles which consists of mixing an aqueous insulating material with said particles, forming a water insoluble dry film on the particles, mixing a second portion 0! said aqueous insulating material with the coated particles, and forming a second water insoluble dry film over said first film.

3. A method of producing a magnetic body from magnetic particles which consists of consecutively applying a plurality of water insoluble insulating coatings to the particles and treating the particles between the applications or the coatings.

. 4. A method of producing a magnetic body from magnetic particles which consists of consecutively applying a-pluraiity of coatings of water laden insulating material to the particles and.

r ndering each coating water insoluble before the application of the following coating.

5. A method of producing magnetic bodies from magnetic particles which consists of consecutively applying a plurality of coatings of a compound containing tartaric acid. sodium silicate, water, and an insulating material to the particles, and evaporating the water to form a water insoluble film on the particle after each coating is applied.

6. A method of producing a magnetic EXAMINER which consists of compounding an insulatingamount of insulating material including soluble ingredients, insoluble ingredients, and tartaric acid, which consists of mixing the magnetic particles with a portion of said insulating material, evaporating the mixture to dryness, repeating this process until all of the insulating material has been used, and forming the particles into a core.

8. A method of producing a magnetic body from particles of magnetic material which consists of compounding an insulating composition -of' an organic acid, sodium silicate and insoluble insulating material, mixing a quantity of the particles with the insulating composition, evaporating the mixture to dryness, mixing the resulting product with a second quantity of the insulating composition and again evaporating the mixture to dryness and forming the resulting product into a core.

9. A method of producing a magnetic body which consists of forming a solution or water, sodium silicate and an organic acid, suspending insoluble insulating material in the solution, mixing the resulting product with particles of magnetic material, evaporating the mixture to dryness to form an insoluble film on the 'particles, mixing the coated particles with a second quantity of the insulating material, and again evaporating the mixture to dryness, and sub-.- sequently forming the material into cores.

10.,A method of producing a magnetic body from a given amount oi. magnetic dust and a given amount of insulating material which consists of applying the insulating material ina plurality of steps and applying a substantially greater amount of insulating material in a subsequent step than applied in a preceding step.

11. A method of producing a magnetic body from finely divided dust particles which consists of compounding an insulating material of solid material, sodium silicate, an organic acid and water, applying a given amountof the insulating material in successive steps and evaporating the coated particles to dryness after each 'application of insulating material.

CHARLES c. NEIGHBORS.

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